For facilitating users to operate electronic devices, a variety of human interface devices are gradually introduced into the market. For example, a keyboard is a widely-used human interface device for controlling a computer. Generally, the keyboard is equipped with plural character keys and plural function keys for generating different signals. According to these signals, corresponding functions of the electronic device can be operated by the user. By depressing one of the character keys, a corresponding letter, number or symbol is inputted. By depressing one of the function keys, a corresponding function signal is generated. Moreover, the function key and a corresponding character key may be combined as a shortcut.
For providing better tactile feel of depressing the keycap of the key, the top surface of the keycap is specially designed to have a downwardly-concave arc-shaped surface for complying with the curvature of the user's fingertip. Moreover, some of the character keys and some of the plural function keys have elongated keycaps. For example, the key “0” of the numeric keypad zone, the enter key or the space key has the elongated keycap.
Since most keycaps are produced by a plastic ejection molding process, the elongated keycaps made of the plastic material may have some drawbacks. For example, since the elongated keycap has a relative long pressing surface, the structural strength of the elongated keycap is usually lower than the structural strength of the ordinary keycap. After the elongated keycap has been pressed for a long time, the elongated keycap is readily damaged. Moreover, since the plastic product is possibly suffered from deformation, the top surface of the elongated keycap may be changed from the downwardly-concave arc-shaped surface to an upwardly-convex arc-shaped surface. Under this circumstance, since the tactile feel of depressing the elongated keycap is deteriorated and the membrane switch under the elongated keycap is difficult to be conducted, the sensitivity of the key is impaired.
For overcoming the above drawbacks, there is a need of providing an improved keycap structure in order to enhance the structural strength of the elongated keycap and correct the deformed top surface of the elongated keycap from the upwardly-convex arc-shaped surface to the downwardly-concave arc-shaped surface.